1. Field of the Invention
The present invention relates to new, low molecular weight, chain-terminated, 5-membered-N-vinyl lactam polymers (oligomers), and more particularly to water-soluble, N-vinyl pyrrolidone polymers (oligomers) functionalized at one end with an hydroxyl, carboxyl or alkoxycarbonyl group; activated derivatives of such compounds and graft copolymers (or conjugates) thereof with drugs and enzymes; and the methods for preparing such products. Chain termination is effected by polymerizing the N-vinyl monomer in an isopropoxy-containing solvent as the chain terminating agent. For grafting the polymer to drugs and enzymes it is most preferable to convert functional moiety (e.g. --OH, --COOH, or --COO (C.sub.1, to alkyl)) to a more "reactive" group for effective grafting or conjugation to the drug or enzyme. Exemplary reagents for this activation include carbonyl di-imidazole, dicyclohexylcarbodiimide (DCC), p-nitrophenyl-chloroformate, 2,2,2,-trifluoroethane sulfonyl chloride, etc.
2. Description of the Prior Art
The availability of amphiphilic oligomers or low molecular weight polymers exhibiting a variety of structures and properties, properly functionalized at the end of the polymer so as to permit the bonding of biological compounds is of great interest inasmuch as it allows the chemical, physical, and pharmacological properties of such biological compounds to be modified. Such polymers find their application in modifications of polypeptides and enzymes (A. Abuchowski and F. F. Davis, "Enzymes as Drugs", J. S. Holcenberg and J. Roberts, Ed., Wiley & Sons, pages 367-384, (1981); F. M. Veronese, Chimica Oggi, pages 53-56, Jan.-Feb. (1989)), and also can be applied in the preparation of "Pro-Drugs" (P. Ferruti and E. Ranucci in "High Performance Biomaterials", M. Szycher, Ed., Technomics Publ., Inc., pages 539-572 (1991)), and in the surface modification of biomaterials.
The modification of enzymes with amphiphilic polymers can, on the one hand, extend their application as biocatalysts in organic solvents, and on the other hand allow for a wider pharmaceutical use of enzymes and polypeptides. It has been observed, in fact, that derivatized enzymes will stay longer in the blood as a result of the combined effects of reduced ultrafiltration and degradation by proteases, diminished immunological reactions, and furthermore may present new targets in the organism.
It has previously been proposed by one of the co-inventors herein to produce low molecular weight N-vinyl pyrrolidone polymers with chain terminating hydroxy and carboxy groups utilizing mercaptoethanol and mercaptoacids, particularly mercaptoacetic acid as the chain-terminating compounds, and reacting same with polysaccharides, and in particular, dextrans to produce a graft copolymer of N-vinyl pyrrolidone and dextran. [F. M. Veronese, L. Sartore, P. Caliceti, O. Schiavon, E. Renucci and P. Ferruti, J. Bioact. and Compat., Vol. 5, pages 167-178 (1990).]
Other techniques which have ben tried include 1) a partial hydrolysis of the lactam rings in the polymer chain leading to the formation along the chain of carboxylic groups, and 2) copolymerization of N-vinyl pyrrolidone with small quantities of functional comonomers such as acrylic acid. The latter two methods lead to multifunctional products, which is not acceptable. Chain termination with mercaptoalcohols and mercaptoacids has not satisfactorily produced the one-end functional oligomers inasmuch as the transfer constant of the mercaptans in the polymerization of the N-vinyl pyrrolidone moiety is very high, and therefore this method results in poorly reproducible products containing large quantities of non-functional polymers of high molecular weight, and only small quantities of the more desirable low molecular weight functional polymers (oligomers).